The invention relates to a brake cylinder for a rim brake and a rim brake comprising such brake cylinders. In particular, the invention relates to a brake cylinder for a hydraulic rim brake for bicycles and a hydraulic rim brake.
A brake cylinder is disclosed in DE 42 32 598 C2.
In the case of the rim brake shown in DE 42 32 598 C2 and comprising the brake cylinders disclosed there, it is difficult to remove the running wheel if the tire mounted on the wheel rim is significantly wider than the wheel rim since the tire has to be moved through the gap between the two brake pads which are arranged on the brake cylinders. Particularly difficult is the removal of the running wheel with the use of the thick tires employed, for example, in mountain bikes.
It is therefore the object of the invention to provide a brake cylinder for a rim brake, or a rim brake, which cylinder or which brake permits easy removal of the running wheel with a simple design of the rim brake.
The object is achieved by a brake cylinder having the features of the embodiments of the invention described herein.
In association with this invention, the direction of the unit for receiving a brake pad denotes a direction tangential to the rim, based on a rim region in which the brake pad makes contact with the rim. This direction is equivalent to the running direction of the rim at the point where the brake pad makes contact with the rim.
In association with this invention, the direction of the main axis of the brake cylinder denotes a direction in which the brake pad is moved toward the rim or away from the rim. As a rule, the brake is operated by displacing a piston in the brake cylinder along the main axis of the brake cylinder.
The design, according to the invention, of the brake cylinder has the advantage that, owing to the rotatable arrangement of the brake cylinder or cylinders, the running wheel can be easily and rapidly removed and reinstalled.
In addition, the brake cylinder according to the invention has the advantage that there is no need for a complicated readjustment of the brake cylinders relative to the rim since the rotation of the brake cylinders returns the brake cylinders to the old setting after reinstallation of the running wheel. This is the case in particular because the brake cylinders need not be detached from the frame for removing the running wheel or defined guidance of the brake cylinders during the rotational movement is ensured. To this extent, the brake cylinder can always be returned to exactly the same starting position after each rotational movement.
A known solution for fastening a brake cylinder of a hydraulic rim brake to frame parts of a bicycle is a two-part adapter comprising a clip-like receiver for the brake cylinder. The adapter is fastened on a cantilever brake base. Degrees of freedom of the orientation of the brake cylinder in all directions for the adjustment of the rim brake are ensured by a spherical receiver.
The known solution has the disadvantages that complicated, expensive parts are used. The parts are moreover heavy and large. The number of parts is large. The mounting of the rim brake requires complicated adjustment work. The complicated adjustment work is also required when reinstalling the running wheel.
The invention provides a brake cylinder or a rim brake, which brake cylinder or which rim brake has at least one feature or any combination of the following features:
1) The brake cylinder is rotatably mounted on the bicycle front fork or on the bicycle rear structure.
2) The axis of rotation is substantially parallel to the fork tube or the seat stay.
3) The rotation is performed about the longitudinal axis of the fork tube or of the seat stay.
4) The axis of rotation is essentially perpendicular to the brake pad.
5) The axis of rotation is inside the brake cylinder. This has the advantage that a very compact design of the brake cylinder can be realized.
6) The axis of rotation is outside the brake cylinder. This has the advantage that the construction of a specific version is simpler because collisions of components during the rotational movement of the brake cylinder can be more easily avoided.
7) When viewed in the direction of travel, the brake cylinder is mounted in front of the supporting part.
8) The brake cylinder offers resistance to the pressures and main braking forces in the force flux in an interlocking manner.
9) The swivelling out of one or both brake cylinders ensures rapid removal of the running wheel.
10) The braking forces in the reverse direction are resisted via a detachable locking means.
11) The rotary means is formed in such a way that defined guidance of the brake cylinder during the rotational movement is ensured. To this extent, the brake cylinders can always be returned to exactly the same starting position after every rotational movement.
12) The degrees of freedom in assembly are limited to an expedient range.
The invention has in particular the following advantages:
Both the brake cylinder and the rim brake as a whole are easily assembled and have few parts.
Furthermore, manufacture is economical and a small construction space is required.
The construction according to the invention leads to a low weight.
The brake cylinder and its fastening can be well integrated visually.
The mounting and removal of the running wheel are rapid and simple.
The brake pad need not be readjusted when the running wheel is reinstalled but is retained.
The mounting of the rim brake or of the brake cylinder is effected in a simple, rapid and unique manner. There is no need for complicated adjustment.
To adjust the position of the free end of the piston inside the cylinder relative to the brake cylinder and hence relative to the rim, it is known that, in the case of rim brakes, hydraulic fluid can be introduced into the pressure space of the brake cylinder by means of a screw on the master cylinder. During this procedure, the piston moves against the action of a spring arrangement in the direction of the rim. By loosening the screw on the master cylinder, hydraulic fluid is withdrawn from the pressure space. Consequently, the piston moves back away from the rim through the force of the spring means.
The free end of the piston is to be understood as meaning that end of the piston which is opposite to the rim of the bicycle in the case of a brake cylinder mounted on a bicycle and, when the brake cylinder is actuated, causes a brake pad to move toward the rim.
In the case of a hydraulic rim brake, usually two brake cylinders are connected to one another by a hydraulic line in such a way that, by operating the brake lever, both brake cylinders are actuated identically and the respective pistons emerge to equal extents from the cylinders. Accordingly, the adjustment of the adjusting screw on the master cylinder results in the simultaneous adjustment of the rest position of the pistons of both brake cylinders. However, there is a need to adjust the setting of the rest position for optimal adaptation of the brake to the rim individually for each brake cylinder.
For example, in the case of disk brakes, it is known that an open system can be used instead of a closed system. An open system means a system comprising a compensating tank which, in the rest position of the brake lever, is connected to the pressure space of the calliper. If the volume of the pressure space is changed by adjustment of the piston in the calliper, a corresponding compensation with hydraulic fluid can be effected by the compensating tank. When the brake is operated, the pressure space is disconnected from the compensating tank. However, an open system has the disadvantage that, owing to the necessity of a compensating tank, it is relatively complicated and hence expensive to manufacture. Consequently, closed systems without a compensating tank are usually used in the case of hydraulic rim brakes.
To be able to adjust the relative position of the free end of the piston with respect to the cylinder independently of the other brake cylinder, the brake cylinder according to the invention preferably has an adjusting device by means of which the relative position of the free end of the piston is adjustable in the axial direction in the cylinder in such a way that the volume of the pressure space remains essentially unchanged. This has the advantage that there is no exchange of hydraulic fluid with the system on adjustment of the free end of the piston in the axial direction relative to the cylinder. Consequently, the adjustment of the free end of the piston can be effected independently of a compensating tank in the case of an individual brake cylinder.
For example, the adjustment of the relative position of the free end of the piston with respect to the cylinder can be effected by means of an adjusting piston which moves the piston (and hence also the free end of the piston) together with the pressure space in the cylinder in the axial direction. As a result, the relative position of the free end of the piston with respect to the cylinder is changed, the volume of the pressure space simultaneously remaining unchanged.
Advantageously, the adjusting piston is screwed into a region of the cylinder. This has the advantage that the adjustment of the free end of the piston can be carried out exactly and reliably.
Advantageously, the distance between the inflow into the pressure space and the adjusting piston in a position furthest away from the inflow is greater than the maximum possible adjustment distance of the adjusting piston. As a result, the possible exchange of hydraulic fluid between the inflow and the pressure space is ensured at all times.
Advantageously, the adjusting piston has a securing ring which limits the maximum possible adjustment distance of the adjusting piston.
For example, the adjustment of the relative position of the free end of the piston with respect to the cylinder can be effected, according to a further embodiment of the invention, by making the piston adjustable in length. This has the advantage that position and size of the pressure space need not be changed during the adjustment of the distance between the free end of the piston and the rim because the relative distance between the free end of the piston and the rim or brake pad and rim can be adjusted merely by adjusting the length of the piston.
A further development of the present invention with one of the devices described for adjustment of the relative position of the free end of the piston with respect to the cylinder results in the further advantage that the brake pad adjustment can be made particularly simply and independently of the adjustment of the brake cylinder. In particular, the distance of the free end of the piston or of the brake pad from the rim of the bicycle can be roughly predetermined by the formation, according to the invention, of the rotatable fastening means and can be finely adjusted by the individual adjustment of the relative position of the free end of the piston with respect to the cylinder of the brake cylinder. This further development results overall in a simple design of the brake cylinder with few parts. In particular, the brake cylinder can be mounted exactly, simply and rapidly on the bicycle.
The further development of the present invention with one of the devices described for adjusting the relative position of the free end of the piston with respect to the cylinder furthermore results in the advantage that the position of the brake pad can be separately set axially and can be adjusted when the pad wears.
According to one embodiment of the present invention, the arrangement member on the rear structure of the frame or the fork with respect to the rim is arranged in such a way that, when the brake cylinder is installed on the arrangement member and when the brake cylinder is rotated to the braking position, the correct position between the brake pad and the rim is automatically established.